Rolling-element bearing

ABSTRACT

A rolling element bearing includes inner and outer rings having raceways and rolling elements between the raceways. The raceways of the inner and outer rings are coated with a first coating, such as a phosphate coating, and the rolling elements are coated with a second, different, coating such as a black oxide coating.

CROSS-REFERENCE

This application claims priority to German patent application no. 102017 222 919.5 filed on Dec. 15, 2017, the contents of which are fullyincorporated herein by reference.

TECHNOLOGICAL FIELD

The present disclosure relates to a rolling-element bearing having aninner ring and an outer ring and rolling elements therebetween where therings and/or the rolling elements include protective coatings.

BACKGROUND

In rolling-element bearings the surfaces of the rings (or of theraceways) as well as of the rolling elements are often coated in orderto achieve a protection of the surfaces or an improved function of therolling-element bearing.

For example, the surfaces, in particular of the rolling elements, can besubjected to a black oxide process such as a bluing in order to producea multifunctional layer that protects the rolling elements. Thisfrequently occurs in connection with fully blued bearings. Bluing offersa reduction of damage mechanisms, for example, a corrosion protection ofthe surfaces. In addition, bluing improves the run-in properties of thesurfaces.

Furthermore, there is the possibility of providing the rolling elementsas well as the bearing rings with a phosphate coating. A sliding orseparating layer is generated by such a phosphate coating between themutually rubbing surfaces of the rolling-element bearing, i.e., betweenthe rolling elements and the raceways.

Both with a bluing and with a phosphate coating the raceways of thebearing rings and the counter-races of the rolling elements are eachcoated with the same system, provided all surfaces are coated. Here thebluing is generated in an alkaline manner and is thus soluble in acid,whereas a phosphate coating is generated acidically and is thusalkali-soluble. A bearing including blued or phosphated surfaces istherefore either only alkaline or acid-resistant. If the rolling-elementbearing is exposed to a corresponding acidic or alkaline environment,the coatings of the surfaces are therefore impaired or eliminated, andthe surfaces of the bearing rings and of the rolling elements cantherefore no longer be held separate from each other depending on thechemical action, i.e., they rub directly against each other or havemetallic contact. The service life of the bearing or of the individualcomponents can thus be reduced.

SUMMARY

It is therefore an aspect of the present disclosure to provide arolling-element bearing, wherein under the most different conditions ofuse a protective layer remains between the surfaces of therolling-element bearing that are moving against each other.

The disclosed rolling-element bearing includes an inner ring and anouter ring between which rolling elements are rotatably disposed. Therolling-element bearing can be a tapered roller bearing, a sphericalroller bearing, a toroidal roller bearing (CARB), a ball bearing, or acylindrical roller bearing.

In order to ensure under the most diverse conditions of use that aseparating surface is present between the surfaces of the rollingelements and the raceways, according to the disclosed rolling-elementbearing it is provided that a raceway of the inner ring and/or a racewayof the outer ring is coated with a first coating, and that the rollingelements are at least partially coated with a second coating, whereinthe first coating and the second coating are different from each other.

Due to the use of two different coatings it can be ensured that underall conditions of use of the rolling-element bearing (e.g., alkaline oracidic environment) one of the two coatings is less worn out than theother. For example, the first coating can be configured resistant toalkali, and the second coating resistant to acid. A protective layerthus always remains between the surfaces of the bearing rings or of therolling elements, which surfaces move against each other.

Furthermore, coatings can be combined that offer different advantages,whereby protection mechanisms of both coatings can be used for therolling-element bearing.

According to one embodiment the first or the second coating is aphosphate coating. The phosphate coating can be, for example, amanganese phosphate coating, a zinc phosphate coating, a zinc calciumphosphate coating, or a tricationic phosphate coating.

The phosphate coating can be applied onto the raceways of the bearingrings or the surfaces of the rolling elements by a rapid and hotprocess. By the process parameters being adapted accordingly withapplying of this coating, a pitting, which can lead to microcrackformation, can be reduced.

According to a further embodiment the first coating is a phosphatecoating, wherein the second coating has a higher hardness than the firstcoating.

This has the advantage that the (somewhat thicker) phosphate coating isapplied onto the bearing rings, whereas the second coating, which can beconfigured thinner, is applied onto the rolling elements. If this wereto be applied onto the rolling elements instead of onto the ringraceways, with a reduction of the thickness of the phosphate coating therolling elements would have too much clearance; the bearing clearancewould thus increase. This would very rapidly be the case since thethickness of the software phosphate coating would be reduced morequickly in comparison to the thickness of the harder second coating.

The second coating can be, for example, a black oxide coating such as abluing. The bluing can have a lesser thickness in the range ofapproximately 1 μm and is of a more stable and thus more incompressiblestructure. In addition, it is a pure oxidation of the substrate and notan overlying layer. On the other hand, the phosphate coating has ahigher thickness of usually a plurality of micrometers and is comprisedof overlying crystal layers including cavities and imperfections,whereby it is compressible under pressure and partially displaceable aswell as less smear resistant. From this it arises that the bluing isharder in comparison to the phosphate coating. Therefore in thefollowing a greater hardness of the bluing is always spoken of.

The phosphate coating forms a porous layer that holds lubricant readylike a sponge. The phosphate coating can also serve as a sliding layer,since it forms a soft layer that is comprised of a plurality of (atleast two) crystal layers, which is displaceable into itself at highload under wear and thus slippery. In addition to the sliding layer thephosphate coating also serves as a separating layer against metalliccontact. In comparison to a bluing the phosphate coating offers asignificantly higher rust protection. Furthermore, the phosphate coatingimproves the running-in behavior of the raceways by filling inunevennesses of the roughness structure of the surfaces.

Furthermore, it can be achieved by the different coatings that one ofthe coatings serves as a sliding and separating layer. At the same timethe rolling elements are coated with a thin different type coating thathas a different hardness. Here the coating of the rolling elementsshould not wear or at least in the event of wear does not generate asignificant dimensional change. In this way it can be ensured that thebearing clearance does not significantly increase even with wear of thecoatings.

According to one embodiment the first coating has a thickness of 1 to 6μm, in particular 2 to 4 μm. This coating thickness is sufficient toensure a protection of the surfaces, but is simultaneously thin enoughto keep the bearing clearance increase to an acceptable amount even withwear or reduction of the phosphate coating.

According to one embodiment the second coating is a carbon layer. Thecarbon layer can be, for example, a DLC layer (diamond-like carbon),such as, for example, a graphite layer, a diamond layer, or an amorphouscarbon layer. A WC/C layer (tungsten carbide carbon) can also beprovided, wherein it is a combination of a metal layer and adiamond-like carbon. Due to this coating the rolling elements areprotected against damage mechanisms and have, for example, wearprotection, dirt tolerance, and favorable friction characteristics.

According to a preferred embodiment the second coating of the rollingelements can be a bluing. With bluing the rolling elements are immersedinto an alkaline solution, by which a conversion layer is formed. Aconversion layer is a very thin layer on a metal surface that isgenerated by the chemical reaction of an aqueous treatment solution (inthis case an alkaline solution) with the metallic base, i.e., thesurface of the rolling elements. Due to this coating the rollingelements are also protected against damage mechanisms.

A bluing offers a very thin coating that is not dimension or tolerancealtering. Unlike with a phosphate coating the thickness of the coatingis not substantially reduced in operation. The bluing is thereforepreferably used for the rolling elements since the thickness of thecoating and thus the dimension of the rolling elements does notsubstantially change in operation and the bearing clearance thereforedoes not increase.

Furthermore, an improved oil adhesion by adhesion on the surface isprovided by a bluing. The bluing further ensures a light rust protectionof the coated surfaces, a reduced friction, and an improved run-inbehavior due to smoothing of the roughness structure of the surfaces. Inaddition, a cold welding between the steel surfaces of the rollingelements and raceways of the rings is prevented and damage mechanismswith a tearing-off lubricating film are prevented. Furthermore, thebluing reduces micropitting, smearing, spalling, friction corrosion,crack formation, and adhesion wear. The bluing also serves as a hydrogenbarrier and prevents an attack by EP additives (extreme pressureadditives).

According to a further embodiment the rolling elements are preferablycompletely coated with the second coating. In this way the rollingelements in their entirety can be protected against damage mechanisms.Furthermore, the manufacturing of completely coated rolling elements issimpler. Since the bluing and/or carbon layer can be configured verythin, the dimensions of the rolling elements can be substantiallymaintained even when the coating is reduced by wear.

According to a further embodiment the raceway of the inner ring and/orthe raceway of the outer ring is completely coated with the firstcoating. Due to a complete coating of the raceway or of the raceways aparticularly good sliding and separating layer can be provided betweenthe surfaces of the bearing rings and of the rolling elements, whichsurfaces move against each other, by the phosphate coating.

The inner ring and/or the outer ring are preferably completely coatedwith the first coating. A better protection of the rings against damagemechanisms, for example, against rust, and thus of the entirerolling-element bearing can be provided by a complete coating of therings. Furthermore, bearing rings having a complete coating are moreeasily and more cost-effectively manufacturable.

Due to water in a lubricating oil used for the rolling-element bearing,surface fatigue, roller flange fretting, and smearing can occur. Thisresults from the fact that water does not form a separating lubricatingfilm, and the lack of a lubricating film or the reduced lubricating filmthickness promotes such wear phenomena. Due to the combination ofraceways including a first coating, namely a phosphate coating, androlling elements including a second coating, namely a black oxidecoating or bluing that has a higher hardness than the first coating, thenegative effect of the water in the lubricating oil can be minimized.For example, the pH value of the lubricating oil can change due to thewater. Since the rolling-element bearing includes coatings thatwithstand different (acidic or alkaline) conditions, only one of thecoatings is attacked by the changed pH value. At least one protectivelayer thus remains between the surfaces of the bearing rings and of therolling elements, which surfaces are moving against each other.

Furthermore, a good sliding and separating layer is provided by thephosphate coating, while simultaneously smearing can be avoided due tothe coated rolling elements. The service life of the bearing can thus beincreased.

Precisely by the combination of two different coatings, in particular ofa phosphate coating and of a bluing, the following advantages can beachieved. The combination of the coatings offers a significantly lowerfriction than a phosphated surface against a further phosphated surface.Furthermore, in operation a clearance increase of the bearing is farless than with the use of two phosphate coatings, since therolling-element set can still add an unfavorable four-fold layerthickness to the clearance.

The outer-lying rings can obtain a higher rust protection due to thephosphate coating; the inner-lying rolling elements can obtain asomewhat lower rust protection due to the bluing. Since the two coatingshave two different mechanisms for holding a lubricant, the lubricant canbe kept in the contact zones in an improved manner. The separation ofthe surfaces is also effected by two different principles.

The different coatings also lead to an improvement in the intake and animprovement of the emergency running properties due to two differenteffects. Furthermore, a protection of the surfaces is effected once by apassive layer (bluing) and once by an overlying protective layer(phosphate coating).

Due to the combination of both coating systems the protective systems ofboth coating types are combined. In this way an improvement of thebearing service life can result in particular under extreme conditionsof use.

Further advantages and advantageous embodiments are specified in thedescription, the drawing, and the claims. Here in particular thecombinations of features specified in the description and in the drawingare purely exemplary, so that the features can also be presentindividually or combined in other ways.

In the following the invention shall be described in more detail usingexemplary embodiments depicted in the drawing. Here the exemplaryembodiments and the combinations shown in the exemplary embodiments arepurely exemplary and are not intended to define the scope of theinvention. This scope is defined solely by the pending claims.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional view of a rolling-element bearing including aninner ring and an outer ring according to the present disclosure.

DETAILED DESCRIPTION

In the following, identical or functionally equivalent elements aredesignated by the same reference numbers.

In FIG. 1 a rolling-element bearing 1 is depicted in a greatlysimplified outline. The rolling-element bearing 1 includes an inner ring2 and an outer ring 4. Rolling elements 6 are rotatably disposed betweenthe two rings 2, 4. Here the rolling elements 6 run against an outersurface 8 of the inner ring 2 as well as an inner surface 10 of theouter ring 4. In order to protect the raceways 8, 10 as well as therolling elements 6 against wear, these are each provided with a coating.Here the coating of the rolling elements 6 can have a greater hardnessthan a coating of the raceways 8, 10. The coating of the rollingelements 6 can be, for example, a bluing.

The ring raceways 8, 10, and preferably the entire rings 2, 4 areprovided with a phosphate coating in order to provide a sliding layerfor the rolling elements 6. In particular, a smearing of the rollingelements 6 can be prevented by the coating of the rolling elements 6.

Here both the phosphate coating and the coating of the rolling elements6 can be configured so thin that even with wear of the coatings thebearing clearance in the rolling-element bearing is increased only in anacceptable range. Since the coating of the rolling elements 6 is harderthan the phosphate coating, the coating of the rolling elements 6 ispreferably not worn and thus remains even with a reduced thickness ofthe phosphate coating as a separating layer between the rolling elements6 and the raceways 8, 10.

Furthermore, a bluing is preferably provided for the rolling elements 6,since this can be applied very thinly. In comparison thereto thephosphate coating is thicker. If the phosphate coating were to beapplied onto the rolling elements 6, with a reduction of the thicknessof the phosphate coating (which occurs very quickly due to the softnessof the phosphate coating in operation) the layer thickness of therolling elements 6 would be reduced and a clearance would be presentbetween the rolling elements 6. In order to prevent the phosphatecoating from rapidly losing layer thickness in operation, which wouldunacceptably increase the bearing clearance, the phosphate coating maynot be applied to all components. Phosphate on rings and rollers wouldgenerate too large a clearance change. The phosphate coating istherefore preferably applied onto the rings since the essential effectsof phosphate, inter alia corrosion protection and prevention of frettingcorrosion, are predominantly required on the rings. The rollers aretherefore provided with a thin and dimensionally stable layer,preferably a bluing. In this way the coatings of the rollers do notadditionally contribute to the phosphate-typical clearance enlargement.

With the disclosed rolling-element bearing it is possible to provide arolling-element bearing that can reduce wear of the rolling-elementbearing under the most diverse conditions of use, for example, even inan acidic or alkaline environment, since at least one of the layers usedremains and thus a protective layer remains between the surfaces of thebearing rings and of the rolling elements, which surfaces move againstone another. Furthermore, due to the two different coatings the runningproperties of the rolling-element bearing can be improved since theadvantages of both coatings can be utilized.

Representative, non-limiting examples of the present invention weredescribed above in detail with reference to the attached drawings. Thisdetailed description is merely intended to teach a person of skill inthe art further details for practicing preferred aspects of the presentteachings and is not intended to limit the scope of the invention.Furthermore, each of the additional features and teachings disclosedabove may be utilized separately or in conjunction with other featuresand teachings to provide improved rolling-element bearings.

Moreover, combinations of features and steps disclosed in the abovedetailed description may not be necessary to practice the invention inthe broadest sense, and are instead taught merely to particularlydescribe representative examples of the invention. Furthermore, variousfeatures of the above-described representative examples, as well as thevarious independent and dependent claims below, may be combined in waysthat are not specifically and explicitly enumerated in order to provideadditional useful embodiments of the present teachings.

All features disclosed in the description and/or the claims are intendedto be disclosed separately and independently from each other for thepurpose of original written disclosure, as well as for the purpose ofrestricting the claimed subject matter, independent of the compositionsof the features in the embodiments and/or the claims. In addition, allvalue ranges or indications of groups of entities are intended todisclose every possible intermediate value or intermediate entity forthe purpose of original written disclosure, as well as for the purposeof restricting the claimed subject matter.

REFERENCE NUMBER LIST

-   1 Rolling-element bearing-   2 Inner ring-   4 Outer ring-   6 Rolling element-   8 Raceway-   10 Raceway

1. A rolling element bearing comprising: an inner ring having a raceway,an outer ring having a raceway, and a plurality of rolling elementsrotatably disposed between the inner ring and the outer ring, whereinthe raceway of the inner ring and/or the raceway of the outer ring iscoated with a first coating, wherein the rolling elements are at leastpartially coated with a second coating, wherein the first coating isdifferent than the second coating.
 2. The rolling-element bearingaccording to claim 1, wherein the first coating or the second coating isa phosphate coating.
 3. The rolling-element bearing according to claim2, wherein the phosphate coating is a coating selected from the groupconsisting of a manganese phosphate coating, a zinc phosphate coating, azinc calcium phosphate coating, and a tricationic phosphate coating. 4.The rolling-element bearing according claim 3, wherein the first coatingis the phosphate coating, and wherein the second coating has a greaterhardness than the first coating.
 5. The rolling-element bearingaccording to claim 4, wherein the first coating has a thickness of 2 to4 μm.
 6. The rolling-element bearing according to claim 3, wherein thesecond coating is a black oxide coating.
 7. The rolling-element bearingaccording to claim 3, wherein the second coating is a bluing.
 8. Therolling-element bearing according to claim 3, wherein the second coatingis a carbon layer.
 9. The rolling-element bearing according to claim 1,wherein the rolling elements are completely coated with the secondcoating.
 10. The rolling-element bearing according to claim 1, whereinthe raceway of the inner ring and/or the raceway of the outer ring arecompletely coated with the first coating.
 11. The rolling-elementbearing according to claim 1, wherein the inner ring and/or the outerring are completely coated with the first coating.
 12. Therolling-element bearing according to claim 1, wherein the phosphatecoating is a coating selected from the group consisting of a manganesephosphate coating, a zinc phosphate coating, a zinc calcium phosphatecoating, and a tricationic phosphate coating, the phosphate coatinghaving a thickness of from 2 to 4 μm, wherein the second coating is abluing, and wherein the rolling elements are completely coated with thesecond coating and the inner ring and the outer ring are completelycoated with the first coating.